This is my table:

i need to write three different types of query:
1.a list of customers that have only Item A
2.list of customers that have item A & B
3.list of customers that have item A & B & C
I am new here i have no idea how to do it,

thank you everyone.

-i tried WHERE EXISTS clause but it does not give the desired result
-tried where clause with IN(‘B’,’C’) but does not work out